It is proposed that radioactive waste generated in the Netherlands be buried underground in Boom clay formations. As this will need to be stored for hundreds of thousands of years it is important that the safety functions of the proposed engineered barriers are well understood. The Dutch repository concept utilises several types of concrete with three main functions: containment of waste (as part of the waste canisters), intermediate buffer (as a backfill material) and mechanical support (as part of gallery lining). Concrete contains many pores which can degrade with long term exposure to Boom clay pore water, which will change the permeability and retention of radionuclides in concrete. We are proposing a SANS experiment to measure the pore distribution in fresh samples and samples which have been exposed to major components of the pore water and artificially aged.